Remotely Operated Vehicles (ROV) such as an unmanned submarine vessel or an unmanned aircraft drone may rely on Direct Current (DC) motors for physical motivation and maneuvering. DC motors may be driven from a DC power source such as a battery.
One such DC motor than provides power sufficient for such operations is a brushless DC motor. Brushless DC motors often use Pulse Width Modulation (PWM) techniques to generate multi-phase (e.g., three-phase) electrical power into the windings of a motor to produce a rotating magnetic field. Other apparatuses like switching power supplies may also use PWM or other switching techniques to generate a regulated output voltage. As a result, an ROV may be equipped with one or more brushless DC motors and/or power supplies that are each driven by a set of multiple (e.g., three) PWM signals generated by a controller for the drive system.
PWM and other switching techniques typically use solid state switching devices such as MOSFET transistors or IGBT transistors. The fast rising and falling edges of pulses from such devices may generate sequences of pulses (e.g., one sequence per phase per motor) with such polarity, amplitude, and duration so as to drive each respective brushless DC motor coil with a specified current waveform, e.g., a sinusoidal current.
However, the very nature of pulses generated from a PWM technique may generate undesirable acoustic noise and electro magnetic interference (EMI) that may be electronically or audibly detected or may interfere with the operation of other circuits that are near the pulse source. For example, a sonar array from a nearby hostile vessel may be able to detect the audible acoustic signature, or an antenna may be able to detect an electronic EMI signature. Similarly, the pulse-induced EMI may cause signal interference on e.g., a microchip, a cell phone, or a radio operated in the vicinity of a PWM-driven, brushless DC motor or switching power supply.
Furthermore, because such EMI may be periodic or predictable in time due to the repeating nature of the pattern of pulses, it may provide a periodic EMI signature that may be detected from a remote location and that may be used to identify the device generating the signature. Yet another negative effect of the PWM technique is the acoustic signature that may be caused by the high speed switching devices. This acoustic signature may be radiated out and be detected or otherwise may interfere with other acoustically sensitive devices in air or in water.